The 3HP compounds of Formula I are useful as stabilizers in organic material normally subject to deterioration caused by heat, light and oxygen. In addition to being antioxidants they are even more useful as intermediates for the preparation of high molecular weight antioxidants for polypropylene and other substrates.
Other methods for the preparation of the aldehydes obtained from the process of this invention are described in British Patent No. 1,455,766 and in U.S. Pat. No. 4,091,225. Both the British and the U.S. Patents claim a process in which 3,5-di-tert.butyl-4-hydroxybenzyl chloride is reacted with isobutyraldehyde under phase transfer conditions. The British Patent describes the product as a red-brown oil, however, the process disclosed in the U.S. Pat. avoids discloration of the product by carrying out the process under an atmosphere of nitrogen.
A difficulty with use of benzyl chloride as taught in the prior art is that a possible coproduct in the preparation of the benzyl chloride is bis(chloromethyl) ether, which is known to be carcinogenic. Thus, it is highly desirable to find other compounds and processes which are capable of forming the desired aldehyde without the use of the benzyl chloride.
The process of the present invention is superior to these in that it produces a light yellow solid product even when carried out in an atmosphere of air. In addition, the art described in the references requires that a mixture of the reactants be added slowly (greater than 2 hours) to the reaction medium. In the process of the present invention it is preferred that the aldehyde not be added until the reaction mixture has been heated to the desired temperature; then the aldehyde may be added in a rapid manner, (10 to 15 minutes), not as taught and disclosed in the prior art references. It has been determined that the aldehyde may in fact be added all at once without having any appreciable effect on either the yield or purity of the desired product.
British Pat. No. 1,455,766 also claims a process in which a 3,5-di-tert.butyl-4-hydroxybenzyl-N,N-dialkyldithiocarbamate is reacted with isobutyraldehyde. The British process gives a higher yield and a purer product than the other processes described. However, the yield is still not as high as that obtained from the process of the present invention.
Another advantage of the process of the present invention over the prior art is that it does not require the use of highly flammable carbon disulfide, one of the reactants needed to form the dithiocarbamate in the above-referenced patent.
The only known reference to 2,6-di-tert.butyl-4-alkoxymethylphenyl in the alkylation of an active hydrogen compound is U.S. Pat. No. 4,014,943. In this patent the compound alkylated is nitromethane and the yield of the product after removing insoluble material is only 65%. U.S. Pat. No. 4,014,943 also teaches the use of equimolar amounts of base and nitro compounds while the process of the present invention can be carried out using as little as 3 mole percent of base.
It is the novel and useful process for the preparation of 3HP compounds using 2,6-di-tert.butyl-4-methoxymethylphenol as a highly effective alkylating agent for aldehydes which have only one hydrogen on the carbon adjacent to the carbonyl group that forms the basis of this invention. The product yields using the processes of this invention are greater than 95% in all cases and the purity of the desired product is high.